Japanese Patent Application Laid-Open Publication No. 2009-84907 (hereinafter referred to as “Patent Literature 1”), for example, discloses a smart entry system that generally comprises a mobile device and a keyless control unit, in which the keyless control unit is connected to a door switch. According to the disclosure of Patent Literature 1, upon detection that a vehicle door has been switched from an opened state to a closed state, the keyless control unit sets a communication area of a request signal to a second predetermined area wider than a first predetermined area. After that, when the mobile device is present in the second predetermined area (i.e., wider communication area), the keyless control unit sets the communication area of the request signal to the first predetermined area. Then, when the mobile device is not present in the first predetermined area (i.e., narrower communication area), the keyless control unit locks the vehicle door.
Namely, immediately after a passenger gets out of the vehicle and then closes the vehicle door, the communication area is set to the wider communication area (i.e., second predetermined area); thus, it is possible to avoid the mobile device from getting out of the wider communication area even when the user tries to hurriedly move away from the vehicle after closing the vehicle door. In other words, even when the user tries to hurriedly move away from the vehicle, the vehicle door can be locked reliably.
However, the inventors of the present invention etc. have recognized that the outer peripheral edge of the first predetermined area (narrower communication area) has to be set at a predetermined distance (e.g., two meters (2 m) or below) from the vehicle, and that, with an approach of lowering transmitter power output of the request signal when the second predetermined area is to be narrowed to the first predetermined area as disclosed in Patent Literature 1, accuracy in setting the first predetermined area would undesirably decrease.
That the outer peripheral edge of the communication area should be set, for example, two meters or below from the vehicle is prescribed by the so-called “Thatcham” that is a standard of Association of British Insurers. According to the disclosure of PCT-Japanese Patent Application Laid-Open Publication No. 2009-532600 (“Patent Literature 2”), for example, distances for defining or setting a communication area are set two meters or below.